Petrole Heater problem

[Dordogne Landlady]

We have used Bluesky petrole heaters for years now with no problems. We buy the petrole in bulk at start of winter. Just put new fuel into all heaters and now they are cutting out with error E4 constantly and we are starting to freeze! Have taken them apart and cleaned all we can think of, bought another bidon of more expensive fuel to try and prove it is not bad fuel we are using but still no go. Anyone else had problems like this. We have 5 heaters and only 1 is performing ok.